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HexPi - my first hexapod! — Parallax Forums

HexPi - my first hexapod!

Bill HenningBill Henning Posts: 6,445
edited 2014-07-12 07:21 in Robotics
I've started blogging about my first hexapod build - controlled by my RoboPi controller (I'll be using a Pi for vision, WiFi, and inverse kinematics)

http://www.mikronauts.com/robot-zoo/hexpi-hexapod-pi-robot/

I'll update it tonight (with what I will accomplish today)

It's nothing like DriverBob's Sci-Fi gigantic bot, but it is the first hexapod I am attempting :)
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Comments

  • mindrobotsmindrobots Posts: 6,506
    edited 2014-04-11 08:58
    Looks like a great start!!

    Multi-channel servo tester?? I think Duane Degn came up with something along those lines using a QuickStart. If that won;t work sounds like another good product for Mikronauts!!

    I'm glad other folks are moving forward on their robot projects - I get to enjoy my hobby vicariously through everyone else!!

    I'm really going to assemble my RoboPi's.....maybe this weekend if all the stars line up and the wind is right....
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-04-11 09:03
    Thanks Rick!

    Wifey insisted that I start to have some fun with bots again instead of just working on consulting projects and products... apparently all work and no play makes for a tired and cranky hubby. Who would've thunk it?

    Actually I've been thinking of making a quick servo tester based on RoboPi today... and who knows, maybe there will be such a product in the future. Depends on how much I like the RoboPi based one.

    Glad to hear you will start to build your RoboPi's! I am looking forward to seeing what you will do with them, and hearing your feedback.
  • DiverBobDiverBob Posts: 1,116
    edited 2014-04-11 09:31
    Bill Henning wrote: »
    I've started blogging about my first hexapod build - controlled by my RoboPi controller (I'll be using a Pi for vision, WiFi, and inverse kinematics)

    http://www.mikronauts.com/robot-zoo/hexpi-hexapod-pi-robot/

    I'll update it tonight (with what I will accomplish today)

    It's nothing like DriverBob's Sci-Fi gigantic bot, but it is the first hexapod I am attempting :)

    It's always good to read about other Hexapods! Good luck with the new toy, even better that the wife did not have to give her permission! I gave up asking for permission, I just ask for forgiveness now... This hobby can definitely get expensive, I started out with a budget on my monster and I'm over that but not too badly. I'm even still inside of my time budget of 3 years to get it walking.

    There are a lot of great information sites out there on IK and software examples that can be used. It would be interesting to see your code when you get to that point.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2014-04-11 10:52
    Here's a link to the QuickStart servo tester.

    I did a lot of programming work on my hexapod a little over a month ago. A couple of things I found useful was calibrating while the servos were connected to the control board. I used the "*" and "/" to change the pulses by 10us and "+" and "-" to change them by 1us.

    Another thing that really helped cut down on brownout resets was to bring the servos online one at a time. All the servos lurching at once causes havoc on the power supply.

    I also made each servo's pin number a variable so they could be assigned from the terminal connection. I got tired of making sure the right servo was connected to the right pin. The pin numbers and the calibration information gets saved to EEPROM so I don't have hard code the data if I don't want to.

    I'm very willing to post my code but it's an absolute mess. I only have a few hundred longs of free space and the IK stuff doesn't currently work. I'm "upgrading" my IK so the 0 degree position of the leg can point in any direction instead of just left or right as seen in the videos. Getting my hexapod up and running again is high on my robotic todo list.
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-04-11 11:08
    Thanks Bob!

    Finding the inexpensive chassis and servo's in China, and trading shipping time for dollars, allowed me to sneak it into my regular toy budget :)

    Shooting for forgiveness.... interesting idea. The only downside is that I fear she would make me build a dog house to sleep in!

    Or worse, build it herself - she is pretty handy with tools.

    I'll have to research IK, right now, I'll be happy when I get all the legs properly calibrated. I am working on making my own servo tester right now, I should be finished with the control panel in a couple of hours. With luck, I hope to have all the legs calibrated today or tomorrow.

    I'll definitely post my experiences and code!
    DiverBob wrote: »
    It's always good to read about other Hexapods! Good luck with the new toy, even better that the wife did not have to give her permission! I gave up asking for permission, I just shoot for forgiveness now... This hobby can definitely get expensive, I started out with a budget on my monster and I'm over that but not too badly. I'm even still inside of my time budget of 3 years to get it walking.

    There are a lot of great information sites out there on IK and software examples that can be used. It would be interesting to see your code when you get to that point.
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-04-11 11:20
    Hi Duane,

    Thank you for the links!

    Your servo tester looks good! I've started a different style tester, where I use pots to control the servo position directly. It will let me try out positions "manually" quickly, for testing the leg limits. I'll use a RoboPi as it already has servo headers and adc. I'll post pics when it works :)

    Your hexapod looks great! The video showing it walking gives me hope I'll have mine walking soon. Nice index at http://forums.parallax.com/showthread.php/135706-Index-Test?p=1049905&viewfull=1#post1049905 btw, thanks.

    I plan to use two independent power supplies. A 5V USB powerbank for the Pi + Prop, and servo's powered by a separate 7.4V LiPo 4000mahr pack (cut down to 6v via two power diodes for now, maybe dc-dc converter later), as I know exactly what you mean about brownouts due to motors.

    We can share code back and forth in this thread (or one of yours if you give me the link).

    I suspect it will be at least mid next week before I am ready to try IK stuff, and after initial experiments I currently plan to move the IK to the Pi - but that plan may change.

    Wifey ordered me to have some fun - and playing with my shiny (literally, silver colored) hexapod is fun!
    Duane Degn wrote: »
    Here's a link to the QuickStart servo tester.

    I did a lot of programming work on my hexapod a little over a month ago. A couple of things I found useful was calibrating while the servos were connected to the control board. I used the "*" and "/" to change the pulses by 10us and "+" and "-" to change them by 1us.

    Another thing that really helped cut down on brownout resets was to bring the servos online one at a time. All the servos lurching at once causes havoc on the power supply.

    I also made each servo's pin number a variable so they could be assigned from the terminal connection. I got tired of making sure the right servo was connected to the right pin. The pin numbers and the calibration information gets saved to EEPROM so I don't have hard code the data if I don't want to.

    I'm very willing to post my code but it's an absolute mess. I only have a few hundred longs of free space and the IK stuff doesn't currently work. I'm "upgrading" my IK so the 0 degree position of the leg can point in any direction instead of just left or right as seen in the videos. Getting my hexapod up and running again is high on my robotic todo list.
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-04-11 16:56
    Update:

    I added two photos to my HexPi page:

    1) current state of assembly

    2) the hexapod parts that came with the kit

    My new "better mousetrap" servo tester is comin galong nicely, now I just have to test it (and write a bit of Spin to make it work).

    I even took the time to mount a RoboPi and the controls on a piece of Sintra. I am already thinking of other uses for it...
  • Paul K.Paul K. Posts: 150
    edited 2014-04-11 17:30
    Great Project. I've built a few of them and they are tons of fun to work on.

    You might want to pick up some bolt thread protectors. A local hardware store should have them. You put them on the ends of the feet which quiets the noise when they walk and give you better traction
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-04-11 18:52
    Thank you Paul for the kind words!

    And the excellent suggestion, bolt thread protectors will work great.

    (oops! wifey just said dinner in a few minutes...)
    Paul K. wrote: »
    Great Project. I've built a few of them and they are tons of fun to work on.

    You might want to pick up some bolt thread protectors. A local hardware store should have them. You put them on the ends of the feet which quiets the noise when they walk and give you better traction
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-04-11 18:55
    I added a photo, and some text, for my attempt at building a servo tester.

    4 thumb joysticks + 4 hat buttons... 8 channels of analog data & 4 digital channels...

    More information at http://www.mikronauts.com/robot-zoo/hexpi-hexapod-pi-robot/

    but here is the pic:
    servo_tester_web.jpg
    800 x 637 - 192K
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-04-12 07:50
    Wifey went shopping... so I am grabbing some time for HexPi :)

    I found my two 7.2V RC battery packs and chargers; I will use them to power the servos for now. Later I will probably switch to two 18650's in series.

    Last night I had a great idea - I will use the thumb sticks switch between two sets of servos for control.

    I am leaning towards getting my servo tester running before I resume assembling HexPi, I think it will save me a lot of time.

    Edit: I added a lot more information on the servo tester on the HexPi page

    http://www.mikronauts.com/robot-zoo/hexpi-hexapod-pi-robot/
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-04-13 07:26
    Sorry guys, I doubt I'll be able to do much on HexPi or the BM servo tester today - wifey is insisting that the weekend is family time.

    I expect several updates on Monday :)
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-04-14 08:58
    I'll be able to work a few hours on HexPi and my "Better Mousetrap" servo tester today :)

    The four joysticks work, the buttons not yet (the modules left off the pull up resistors) - details on my HexPi page. I'll update it several times today.

    http://www.mikronauts.com/robot-zoo/hexpi-hexapod-pi-robot/
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-04-14 17:32
    I've posted three updates on my HexPi article since my last post in this thread.

    Quick summary:

    - I had to add pull-up resistors to the switches on thumbstick pcb's, the manufacturer left them off
    - joystick calibration now works
    - Kentucky Fried Servo!!! (defective servo found in my last order)

    As usual, far more detail at:

    http://www.mikronauts.com/robot-zoo/hexpi-hexapod-pi-robot/

    I plan on posting some pics tonight.
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-04-23 15:07
    HexPi has been feeling lonely & abandoned...

    I've been too busy with other work, so no progress yet. It looks like I might have a few hours for HexPi tomorrow.

    Sorry about the lack of updates.
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-05-21 10:10
    I'm back working on HexPi after a fantastic three week vacation!

    I dismounted the three legs I previously mounted on HexPi, as I want to re-calibrate all the "pelvis/shoulder" servos. It turns out that my initial idea of where to center the legs was sub-optimal.

    This time, I am going to pay attention to the limits to travel imposed by the servo holders. Later, I may remove some metal from the servo mounts to allow for greater freedom to travel - I consider the unnecessary travel limits to be a design flaw, caused by using off-the-shelf brackets for the hips. I'll take some photos to illustrate what I mean later.

    I might even add some limit switches to detect leg collisions, and footpad switches to detect when the leg is on the surface the robot is travelling on.

    Meanwhile, I added support for the inexpensive HC-SR04 distance sensor to the RoboPi firmware, object, and library, so I will mount one or two on HexPi. (I am also adding Ping and SeeedStudio range sensor support).

    The "Better Mousetrap" servo tester is working, I plan on posting some photos (and maybe videos) of it working soon. It is really nice to be able to test up to eight (soon 16) servos at once.
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-05-21 11:52
    All six "pelvis/shoulder" servos are calibrated, and the chassis is now fully assembled.

    Time to start adding and calibrating the legs :)

    Once I add the legs, I'll add the battery packs, and RoboPi for initial testing (the Raspberry Pi will be added later).
  • DiverBobDiverBob Posts: 1,116
    edited 2014-05-21 16:10
    Good job! Glad to see you hitting it again, there's always something to pull you away from the hobbies! It's a lot harder to motivate yourself with nicer weather now also.
  • ercoerco Posts: 20,257
    edited 2014-05-21 17:25
    Looks great, Bill. I was very interested to see that you chose TowerPro MG995 servos. I haven't used those previously, but two came with my latest robot arm kit from China, waiting to be built:

    http://www.ebay.com/itm/160998716216?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2648#ht_1486wt_929

    I was worried when I saw the terrible review of them below, describing them as "the worst servos I've ever seen - bar none!" .

    Ack! Have you tested yours? I saw you got one Kentucky fried servo.

    http://www.rcmodelreviews.com/mg995review.shtml

    Edit: At least that reviewer likes my favorite 9g servo, Hobby King's HXT900: http://www.rcmodelreviews.com/chineseservos1.shtml
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-05-21 17:55
    Thanks Bob!

    I know what you mean - wifey kidnapped me for a three week vacation. Loved it.

    I did miss my lab and good internet access, but there was something liberating in being away from work / computers / internet / tv as well.
    DiverBob wrote: »
    Good job! Glad to see you hitting it again, there's always something to pull you away from the hobbies! It's a lot harder to motivate yourself with nicer weather now also.
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-05-21 18:03
    Thank you!

    Wifey would have kicked me out if I spent $1K on a hexapod bot. Or at least put me in a dog house she would have me build.

    I know the reviews are bad, but I had to work within my toy budget.

    - Cheap Futaba S3003's did not have enough torque

    - the chassis vendor said minimum servos were the MG995's

    My experience (summary)

    - ordered 50 MG995's (enough for two hexapods + spares)
    - one went up in smoke
    - one did not work (I was able to fix it, loose GND wire due to cold solder joint)
    - four had one broken off mounting tab (three were still ok), one of these was the "kentucky" servo
    - rest tested OK, have not tested for accuracy yet

    As nearly as I can tell, the real problem is lack of quality control at the factory. There is NO way the servos were tested at the factory, if they had been, I'd have received 50 working servos.

    Given that I could repair one of the servos, I got 49 usable servos (from a shipment of 50).

    So my experience so far is better than the review, however I will know much better once HexPi is walking around.
    erco wrote: »
    Looks great, Bill. I was very interested to see that you chose TowerPro MG995 servos. I haven't used those previously, but two came with my latest robot arm kit from China, waiting to be built:

    http://www.ebay.com/itm/160998716216?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2648#ht_1486wt_929

    I was worried when I saw the terrible review of them below, describing them as "the worst servos I've ever seen - bar none!" .

    Ack! Have you tested yours? I saw you got one Kentucky fried servo.

    http://www.rcmodelreviews.com/mg995review.shtml
  • ercoerco Posts: 20,257
    edited 2014-05-21 19:51
    Some RC guys come down hard on servos that have unsupported boards or internal components which might fatigue and break from vibration when used on a big gas-powered airplane. Much less critical in robotic apps for obvious reasons. We need torque, durability, and accuracy.
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-05-22 11:26
    I can see their point of view when it comes to big, expensive planes... they need fewer servos, and can't live with issues.

    A robot has far less altitude to fall from :)
    erco wrote: »
    Some RC guys come down hard on servos that have unsupported boards or internal components which might fatigue and break from vibration when used on a big gas-powered airplane. Much less critical in robotic apps for obvious reasons. We need torque, durability, and accuracy.
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-05-22 11:28
    I've added some more photos of the assembled chassis to my HexPi build log, you can find them at:

    http://www.mikronauts.com/robot-zoo/hexpi-hexapod-pi-robot/

    Here is a teaser pic :)

    hexpi-chassis-0689-web.JPG
    hexpi-chassis-0689-web.JPG
    800 x 530 - 117K
  • ercoerco Posts: 20,257
    edited 2014-05-22 14:00
    Paul K. wrote: »
    Great Project. I've built a few of them and they are tons of fun to work on.

    Understatement of the year! Paul K is apparently too modest to blow his own horn, so please allow me. Brother Paul has worked wonders on his Propeller-based IK hexapod. See his thread at http://forums.parallax.com/showthread.php/126747-Propeller-Based-IK-Hexapod-Project

    and his video below.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2014-05-22 14:04
    erco wrote: »
    Understatement of the year!

    +1

    I'm still actively working on the hexapod Paul gave me.

    Thanks for the updates Bill. It's fun to follow along.
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-05-22 16:10
    Erco,

    Thanks for the links and the video! That code should work on my bot with very few modifications... I'll have to check out the rest of Paul's stuff.

    I even have a PS2 writeless controller just like the one Paul used - got it from RobotShop.ca just before I went on vacation. Fortuitous coincidence!
    erco wrote: »
    Understatement of the year! Paul K is apparently too modest to blow his own horn, so please allow me. Brother Paul has worked wonders on his Propeller-based IK hexapod. See his thread at http://forums.parallax.com/showthread.php/126747-Propeller-Based-IK-Hexapod-Project

    and his video below.
  • Bill HenningBill Henning Posts: 6,445
    edited 2014-05-22 16:14
    Hi Duane,

    Agreed, hexapods are fun - and I don't even have mine running! Loved looking at Paul K's video, and checked his thread - found useful source code :)

    Funny story:

    I asked my 14 year old niece ... "Would you be scared of my large robot spider?"

    She got a thoughtful look on her face... thought about it for about half a minute... and said ... "Maybe."

    Honest little girl!

    I got the brushed aluminium chassis so it would be less likely to scare my niece and nephews. I will also avoid mounting clacking pincers...
    Duane Degn wrote: »
    +1

    I'm still actively working on the hexapod Paul gave me.

    Thanks for the updates Bill. It's fun to follow along.
  • ercoerco Posts: 20,257
    edited 2014-05-22 23:32
    Is this the controller you fellows have?

    http://www.ebay.com/itm/Wireless-Controller-Receiver-Refit-DIY-for-Arduino-Robot-Walking-Biped-Spider-/271172571133?pt=Radio_Control_Parts_Accessories&hash=item3f23250ffd
  • WhitWhit Posts: 4,191
    edited 2014-05-23 06:25
    Very nice and very complex project Bill! Thanks for sharing all the steps...
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